The GEANT SimulationPackage and its use inCompton Telescope Design

The GEANT SimulationPackage and its use inCompton Telescope Design

R. Marc KippenSpace and Remote Sensing Sciences GroupLos Alamos National Laboratory

Astronomy with Radioactivities IV May 26–30, 2003 – 2 –R. Marc Kippen

The Role of Simulation in DesignThe Role of Simulation in Design

+ =

: Realistic componentperformance

6 Expensive and timeconsuming

6 Inflexibleconfiguration

6 Unrealisticenvironment

: Inexpensive andcomparatively rapid

: Flexibleconfiguration

: Flexible environment6 Must model the

componentperformance

MEGA Prototype

Prototypes, Balloons, etc.

MEGA Prototype Simulation Model

Simulations, Models, etc.

MEGA Flight Concept

Scientific Mission

n Successful flightexperiment, where:® Realistic estimates

of performancehelp “sell” themission

® Instrument designis optimized forscientific missionand environment

Astronomy with Radioactivities IV May 26–30, 2003 – 3 –R. Marc Kippen

Simulating Compton TelescopesSimulating Compton Telescopes

n Analytical modeling ofCompton imager physicalresponse is impractical due tocomplexities of geometry,scattering, and secondaryproduction

n The most viable approach isMonte Carlo radiation transportsimulation — probabilistictracking individual “testparticles”

n Other simulations important toinstrument design: mechanical,thermal, electronics, etc.

PhotonsElectrons

Astronomy with Radioactivities IV May 26–30, 2003 – 4 –R. Marc Kippen

Instrument Simulation FrameworkInstrument Simulation Framework

ScienceGoal

Inputs

BackgroundInputs

OrbitalEnvironment

Model

PhysicalSimulation

Engine

InstrumentMass Model

SpacecraftMass Model

Test Dataand/orModels

InstrumentalEffects Engine

Data Processingand Analysis

Mechanical Model(s)

Physics Data/Models

SciencePerformanceEvaluation

AuxiliaryData/Models

Iterate at All Levels

Credible Simulation Requires Credible Inputs at All Levels

Astronomy with Radioactivities IV May 26–30, 2003 – 5 –R. Marc Kippen

n Requirements for ComptonTelescope simulations:

® Detailed electromagnetic physicsfor direct telescope response(~1 keV – 100 MeV)

® Competent hadronic cascadephysics for simulation of promptcosmic-ray–induced background

® Isotope excitation and radioactivedecay for simulations of delayedactivation-induced background

® Convenient and flexible handlingof complex geometry andmaterials for rapid design studies

® Modern, modular architecturethat allows customization

Monte Carlo Radiation Transport PackagesMonte Carlo Radiation Transport Packages

n The particle and nuclearphysics communities havedeveloped several “general-purpose” Monte Carlo transportpackages, including:

® EGS® FLUKA® HETC/MORSE/MICAP® CALOR® MCNP/MCNPX® GEANT/GEANT4

Astronomy with Radioactivities IV May 26–30, 2003 – 6 –R. Marc Kippen

Capabilities of GEANT4Capabilities of GEANT4

n GEANT := GEometry And Tracking

n Complex 3D geometry, materials,MC transport, and visualization inone package

n Developed & maintained by CERN+ large collaboration

n Modern, object-oriented (C++)“toolkit” architecture

n Comprehensive (nearly) suite of EMand hadronic physics

n Straightforward installation and useon many platforms® Wintel, Sun, HP, Linux, Darwin

n ESA Space Specific Modules

n General Source Particle Module® Tookit for input spatial/spectral sampling

n Radioactive Decay Module® Provides the capability to model

activation-induced background inorbit

® Uses detailed Evaluated NuclearStructure Data Files

n Low-energy EM physics® Uses detailed cross sections from LLNL

Evaluated Photon/Electron/Atomic DataLibraries

® Applicable above ~250 eV® Ties X-ray and Gamma-ray applications

´ Important omission: electronbinding effects in Compton

geant4.web.cern.chgeant4.web.cern.ch www.space.qinetiq.comwww.space.qinetiq.com

Astronomy with Radioactivities IV May 26–30, 2003 – 7 –R. Marc Kippen

Effects of Atomic Electron BindingEffects of Atomic Electron Binding

n Suppresses forward scattering,particularly at low energies

n Suppresses total scatteringprobability at low energies

0.4

0.3

0.2

0.1

0.0

sto

t (cm

–1)

10 100 1000 10000

Photon Energy (keV)

Atomic Silicon

Free e- Atomic e-

0.08

0.06

0.04

0.02

0.00

ds/d

W (b

arn

· sr–1

)

1801501209060300

Photon Scatter Angle (deg)

Atomic Silicon

100 keV

Free e- Atomic e-

n GEANT4 Low-energy Compton process includes these effects

†

d2sdWdk

Ê

Ë Á

ˆ

¯ ˜

i

=ro

2

4k f kko

2

Ê

Ë Á

ˆ

¯ ˜

k f

ko+

kok f

- sin2 jÊ

Ë Á Á

ˆ

¯ ˜ ˜

dpz

dkJi pz( )

Astronomy with Radioactivities IV May 26–30, 2003 – 8 –R. Marc Kippen

Doppler Broadening Physics & EffectsDoppler Broadening Physics & Effects

1.0

0.8

0.6

0.4

0.2

0.0

Norm

alize

d Av

erag

e J(

Q)

-30 -20 -10 0 10 20 30Bound Momentum Q (keV/c)

Compton ProfilesJ(Q)

CZTHWHM = 4.5 keV/c

SiliconHWHM = 2.1 keV/c

k = ko -kokEo

1 - cosj( ) - pz ko - k

For bound atomic electron:

kfree = ko -kok

moc2 1 - cosj( )

For free electron: pz = 0 ; Eo = moc2

†

fi Dk = k - kfree; Dj = j -j free

Doppler broadening error:

jko

k

Eo, pz

E, p

Biggs,Mendelsohn,& Mann (1975)

14

12

10

8

6

4

2

0

Scat

ter A

ngle

Erro

r (de

g)

1801501209060300Scatter Angle (deg)

CZT Silicon

100 keV

1 MeV

Astronomy with Radioactivities IV May 26–30, 2003 – 9 –R. Marc Kippen

GLECS & G4LECSGLECS & G4LECS

n GLECS = GEANT Low-Energy Compton Scattering® Thanks to Doug Swartz (USRA, Huntsville) for early help

n Incorporates Doppler broadening into GEANT & GEANT4

n Algorithm based closely on EGS Implementation® Namito, Ban, & Hirayama, NIM A349, 489 (1994)® Relativistic impulse approximation (ignore atomic electron interactions)® Uses EPDL for total cross sections® Uses EPDL differential cross sections (scattering form factors)® Uses shellwise Compton profiles (Biggs, Mendlesohn, & Mann 1975) to

sample Doppler broadened scattered photon energies® Also fixes Rayleigh (coherent) scattering physics with EPDL data® Computing performance within 5% of G4LowEnergy classes

n Soon to come: combined polarization and Doppler broadening

Astronomy with Radioactivities IV May 26–30, 2003 – 10 –R. Marc Kippen

Verification of G4LECSVerification of G4LECS

n G4LECS compared to synchrotron beam experiment® Namito, Ban, Hirayama, et al. (1994, 1995)

Experiment(Polarized Beam)

Simulation(Unpolarized Beam)

Astronomy with Radioactivities IV May 26–30, 2003 – 11 –R. Marc Kippen

Test ResultsTest Results

10-6

10-5

10-4

10-3

10-2

Coun

ts (p

eak

norm

alize

d)

403836343230

Scattered Energy Deposition [keV]

Data (Namito et al.) G4LECS Simulation G4LowEnergy Simulation

v4.4.1

Carbon 40 keV

10-6

10-5

10-4

10-3

10-2

Coun

ts (p

eak

norm

alize

d)

403836343230

Scattered Energy Deposition [keV]

Data (Namito et al.) G4LECS Simulation G4LowEnergy Simulation

v4.4.1

Copper 40 keV

10-6

10-5

10-4

10-3

10-2

Coun

ts (p

eak

norm

alize

d)

403836343230

Scattered Energy Deposition [keV]

Data (Namito et al.) G4LECS Simulation G4LowEnergy Simulation

v4.4.1

Lead 40 keV

n Good agreement in Compton andRayleigh peaks (and Ge-K escape)

n Some differences in multi-Compton continuum probably dueto approximated geometry

Astronomy with Radioactivities IV May 26–30, 2003 – 12 –R. Marc Kippen

Application to Compton Telescope DesignApplication to Compton Telescope Design

Doppler Limit Angular ResolutionZoglauer & Kanbach, Proc. SPIE 4851, 1302 (2003)

Astronomy with Radioactivities IV May 26–30, 2003 – 13 –R. Marc Kippen

Telescope Design Study ExampleTelescope Design Study Example

Si + CZTmulti-scatterDesign

14121086420An

gula

r Res

. (FW

HM, d

eg)

10 100 1000 10000Energy (keV)

100¥100 cm2

NoDoppler

10-3

10-2

10-1

100 E

2 • Se

nsitiv

ity (k

eV ·

cm-2 s

-1)

10 100 1000 10000Energy (keV)

1 Msec

BATSECOMPTEL

New Design

Astronomy with Radioactivities IV May 26–30, 2003 – 14 –R. Marc Kippen

http://nis-www.lanl.gov/~mkippen/actsim/

actsim@lanl.gov

http://nis-www.lanl.gov/~mkippen/actsim/

actsim@lanl.gov